Fix incorrect line numbers in logs

Because beets wraps `logging.Logger`, the default `stacklevel=1`
incorrectly reports all log messages being emitted from
`beets/logging.py:163` at the `super()._log()` callsite. Change the
default to `stacklevel=2` so that the reported line numbers in debug
logging are the actual logging callsites.

Signed-off-by: Ross Williams <ross@ross-williams.net>

beets/logging.py

@@ -152,7 +152,7 @@ class StrFormatLogger(Logger):
         exc_info: _ExcInfoType = None,
         extra: Mapping[str, Any] | None = None,
         stack_info: bool = False,
-        stacklevel: int = 1,
+        stacklevel: int = 2,
         **kwargs,
     ):
         """Log msg.format(*args, **kwargs)"""